Polyester resin emulsion and two-component aqueous paint

ABSTRACT

The present invention relates to a hydroxy-functional polyester resin, which is obtainable by reaction of a composition, which contains (i) a low-molecular polyvalent alcohol having at least two hydroxyl groups per molecule, (ii) a polyether polyol, (iii) a monofunctional saturated aliphatic, cycloaliphatic or aromatic carboxylic acid, and (iv) a polycarboxylic acid having at least two carboxyl groups. The invention further relates to a resin emulsion and a mother paint comprising an aqueous emulsion of the polyester resin, a two-component water-based paint system, comprising the resin emulsion or the mother paint and an isocyanate component as well as a method for the preparation of the water-based paint system.

The invention relates to a polyester resin, an aqueous polyester resinemulsion, a two-component water-based paint system as well as a methodfor the preparation thereof.

Due to ecological problems and the associated pressure to reduce solventemissions, water-based paints have widely spread in different areas andhave substituted solvent-containing paint materials in many cases.

Aqueous two-component polyurethane systems have proven themselves foryears in areas with high demands to weatherability, protection againstcorrosion and resistance to chemicals. These two-component systemsconsist of a polyol and an isocyanate component, which are mixed only ashort time before processing.

One-component and two-component paints differ in particularsignificantly in quality from one another. Two-component polyurethanepaints are clearly superior to air-drying one-component paints in boththe mechanical properties, such as elasticity and hardness, as well asthe resistance to weather, solvents and influences of the environment.

Oligomeric isocyanates, for example based on hexamethylene diisocyanateor isophorone diisocyanate, are mainly employed as isocyanatecomponents. Hydroxy-functional acrylate dispersions, hydroxy-functionalpolyester and alkyd resins as well as hydroxy-functional polyurethanedispersions are in principle suitable as polyol components.

The spreading of these paint systems continues to increase for examplein paints for vehicles as well as in paints for plastics, furniture andin industry.

However, a wide spreading has been hampered in many cases by the problemof a lack of reproducibility of the process. Under unfavorable curingconditions, for example unfavorable climatic conditions (high humidity),the formation of bubbles occurs during drying due to CO₂ developmentfrom the side reaction of the isocyanate with water. In particular, athigh layer thicknesses this results in undesired formation of bubbles inconnection with unevenness of the surface. According to the conditionsfor drying, depending on temperature and humidity, such systems allowfor the reproducible preparation of layer thicknesses of at most 60 to80 μm.

An alkyd resin system is described in DE-A-198 22468 which ischaracterized by a low tendency towards formation of bubbles andtherefore improved process reproducibility. However, due to an albeitlow tendency towards yellowing caused by the oil components containedtherein, this system is not suitable for applications with the highestdemands to product properties, for example weatherability, protectionagainst corrosion and resistance to chemicals or mechanical properties,such as encountered for example in the area of automotive coating andrepair paints.

A further disadvantage of known paint systems based on alkyd resins ofnatural oils is an albeit only very low decrease of the degree of glossand/or change of the mechanical properties of the paint layer undercommon aging conditions (in particular exposure to parts of theUV-radiation spectrum and/or elevated temperature), which may havenegative effects in applications with the highest demands.

The object of the present invention is to provide a resin system for atwo-component water-based paint system, which is characterized by an atmost low tendency towards the formation of bubbles and which fulfillseven the highest demands regarding the tendency towards yellowing andweatherability. In the long term, the degree of gloss and/or themechanical properties should not experience a significant reduction,either.

The resin system should preferably be stably dispersible in waterwithout the use of organic solvents or at most with a low fraction ofsolvents, in order to obtain paint systems with favorable VOC values.

This object is achieved by the subject-matter of the present invention.The invention refers to a hydroxy-functional polyester resin for theapplication in two-component water-based paint systems, which isobtainable by reaction of a composition, containing

-   -   (i) at least one low-molecular, polyvalent alcohol having at        least two hydroxyl groups per molecule,    -   (ii) at least one polyether polyol,    -   (iii) at least one monofunctional saturated aliphatic,        cycloaliphatic or aromatic carboxylic acid, and    -   (iv) at least one polycarboxylic acid having at least two        carboxyl groups per molecule.

The invention further refers to a resin emulsion, comprising an aqueousemulsion of the polyester resin, as well as a mother paint comprisingthe resin emulsion and one or more additives, selected from the groupconsisting of pigments, fillers, auxiliaries and cosolvents.

Furthermore, the present invention refers to a two-component water-basedpaint, which comprises the aqueous emulsion of the hydroxy-functionalpolyester system and an isocyanate component.

The invention further refers to a method for the preparation of atwo-component water-based paint system, which comprises the steps of:

providing a polyester resin component (A) by

-   -   (a) reacting of a composition, containing at least one        low-molecular, polyvalent alcohol having at least two hydroxyl        groups per molecule, at least one polyether polyol, at least one        monofunctional saturated aliphatic, cycloaliphatic or aromatic        carboxylic acid, and at least one polycarboxylic acid having at        least two carboxyl groups to obtain a hydroxy-functional        polyester resin,    -   (b) neutralizing the hydroxy-functional polyester resin with        ammonia or amine,    -   (c) emulsifying the hydroxy-functional polyester resin in water,        and    -   (d) optionally adding one or more additives, selected from the        group consisting of pigments, fillers, auxiliaries and        cosolvents, as well as        providing an isocyanate component (B).

The aqueous paints according to the present invention are suitable fordifferent substrates, such as metal, plastic or wood, and are thereforesuitable for both ground coatings and fillers as well as top coatingpaint systems.

The system according to the present invention is characterized by a verylow sensitivity to bubbles, so that layer thicknesses of 120 to 150 μmand more can be obtained without the undesired formation of bubbles.

Furthermore, the system according to the present invention ischaracterized by a high UV-resistance. This allows for the preparationof paint systems, which are adequate for applications with the highestdemands. In particular, problems which may be caused by a change of thepaint layer due to the impact of UV-radiation, for example changes inthe mechanical properties and brittleness, but also optical changes,such as yellowing can be reduced to a minimal extent or can even beprevented.

The two-component water-based paint systems of the present inventionpossess a high storage stability. Furthermore, the use of ecologicallyharmful or toxic solvents can be avoided.

As compared to conventional water-based paint systems based on alkydresins of natural fats and oils, the water-based paint systems of thepresent invention have the further advantage of a more preciseadjustability of the properties of the end product.

Since natural fats and oils are mixtures the composition of which is notcompletely known and which can be subject to natural variations, smallproblems with regard to the reproducibility of the exact composition mayresult. These problems can be circumvented by the systems of the presentinvention. Furthermore, a wider spectrum of variations of the desiredproperties of the end product results, which can be adjusted in atarget-oriented and reproducible manner.

The paint systems of the present invention provide paint layers with ahigh and stable gloss.

Polyester Resin Component (A)

The polyester resin component (A) according to the present inventioncomprises an aqueous emulsion of a hydroxy-functional polyester resin,which is obtainable by reaction (polycondensation, esterification) of analcohol component and an acid component.

The alcohol component contains (i) at least one polyvalent,low-molecular alcohol having at least two hydroxyl groups and (ii) atleast one polyether polyol.

The acid component contains (iii) at least one monofunctional, saturatedaliphatic or cycloaliphatic or aromatic carboxylic acid and (iv) atleast one polycarboxylic acid having at least two carboxyl groups.

The polyester resin component according to the present invention ischaracterized by not containing any ethylenically unsaturatedmonofunctional carboxylic acid moieties. In a preferred embodiment noneof the components (i) to (iv) employed for the preparation of thepolyester resin have an ethylenically unsaturated character.

Polyvalent Alcohol (i)

Suitable polyvalent alcohols (i) are saturated, aliphatic alcoholshaving at least two, preferably more than two, hydroxyl groups permolecule. In the present invention compounds which are eithermonomolecular or have a very low degree of oligomerization, for exampledi-, tri- or tetramolecular compounds, are considered to below-molecular alcohols. Such low-molecular compounds usually have amolecular weight of less than 400, preferably less than 200.

It is particularly preferable to use alcohols which have at least two,in particular more than two, but not more than six hydroxyl groups permolecule. Typical alcohols (i) have 2 to 20, preferably 2 to 8, carbonatoms.

Examples of suitable polyvalent alcohols (i) are

-   -   divalent alcohols of the general formula        OH—(R)—OH        wherein R is a divalent saturated aliphatic or cycloaliphatic        hydrocarbon group, which may contain one or more (preferably not        more than 4) oxygen atoms, which do not form a peroxide moiety,        and preferably 2 to 20, more preferably 2 to 8 carbon atoms,        such as ethylene glycol, diethylene glycol, propylene glycol,        dipropylene glycol, butylene glycol, dibutylene glycol or        neopentyl glycol;    -   higher valent alcohols of the general formula

wherein n, m and p are independently 0, 1, 2 or 3, and R¹ is a saturatedaliphatic or cycloaliphatic C₁-C₆ hydrocarbon group or an OH—(CH₂)_(q)—group, wherein q represents 0, 1, 2 or 3 (with the proviso that q and mare not simultaneously 0), such as glycerine, trimethylol ethane,trimethylol propane or pentaerythritol;

-   -   other higher valent alcohols, such as cyclohexanediol, threitol,        erythritol, arabitol, adonite, xylite, dipentaerythritol,        sorbite, mannitol and dulcitol.

Of course, mixtures of these alcohols may also be used.

In a preferred embodiment of the present invention at least twodifferent multivalent alcohols are used as component (i). The mixture isto be preferably selected such that the average functionality is atleast 2.0, preferably more than 2.0, in particular 2.1 to 4.5.

A composition in which the amount of the component (i) is about 10 to 40wt. % based on the sum of all components (i) to (iv) is preferably usedfor the preparation of the polyester resin.

Polyether Polyol (ii)

Higher-molecular polyether polyols (ii), such as polyethylene glycol,polypropylene glycol and polytetrahydrofurane, are incorporated tofacilitate emulsification in addition to the low-molecular polyalcohols(i) mentioned. In contrast to the alcohols employed as component (i),the polyether polyols are polymeric substances with a degree ofpolymerization of typically more than 8, preferably 50 to 200. Thepreferred molecular weight of the employed polyether polyols is 400 to8000, in particular 1000 to 6000. Mixtures of the polyether polyols areincluded according to the present invention.

A composition in which the amount of the component (ii) is about 3 to 15wt. % based on the sum of all components (i) to (iv) is preferably usedfor the preparation of the polyester resin.

Monocarboxylic Acid (iii)

The monocarboxylic acids (iii) of the present invention may be saturatedaliphatic, cycloaliphatic or aromatic compounds. Therefore, basicallyall conventional carboxylic acids are suitable as component (iii), aslong as they do not have any ethylenically unsaturated moieties. Theycan be used separately or as a mixture.

Suitable monocarboxylic acids are for example those of the generalformulaR²—COOR′wherein R² is an aromatic, optionally substituted by straight-chain orbranched alkyl groups, hydrocarbon group or a straight-chain or branchedsaturated aliphatic or cycloaliphatic hydrocarbon group preferablyhaving 6 to 30 carbon atoms, in particular 6 to 18 carbon atoms, and R′may be a hydrogen atom (free acid), a straight-chain or branched C₁-C₄alkyl group (ester) or —(CO)R² (anhydride).

Typical examples therefor are isodecanoic acid, isooctanoic acid,cyclohexanoic acid, benzoic acid, p-tert-butylbenzoic acid andlong-chain carboxylic acids as well as naturally occurring saturatedfatty acids.

Examples for naturally occurring saturated carboxylic or fatty acids arepalmitic and stearic acid. However, technically completely hydratedmodifications of natural, unsaturated fatty and oil acids are also wellsuited.

Furthermore, carboxylic acids may also be used, which contain anadditional hydroxyl group in addition to the carboxyl group, such as isthe case for example in the fatty acid of castor oil, indimethylolpropionic acid or in hydrolyzed, epoxidized fatty acids.

For the preparation of the polyester resin, the monocarboxylic acids maybe used in form of the free acids, anhydrides thereof or in form ofesters of simple alcohols (for example C₁-C₄ monoalcohols).

In the present invention, saturated aliphatic or cycloaliphaticmonocarboxylic acids are preferably used.

The component (iii) consists of a mixture of at least two differentmonocarboxylic acids in a particularly preferred embodiment.

A composition in which the amount of the component (iii) is about 10 to40 wt. % based on the sum of all components (i) to (iv) is preferablyused for the preparation of the polyester resin.

Polvcarboxylic Acid (iv)

The polycarboxlic acids used in the present invention have at least twocarboxyl groups per molecule and may be used separately or as a mixture.

Suitable polycarboxylic acids have 4 to 15, preferably 4 to 10, carbonatoms per molecule and include aliphatic, cycloaliphatic and aromaticpolycarboxylic acids.

Surprisingly, in contrast to the monocarboxylic acids (iii) used in thepresent invention the polycarboxylic acids (iv) may have anethylenically unsaturated character, without any negative effects on theUV-stability.

Suitable acids (iv) are for example dicarboxylic acids of the generalformulaHOOC—R³—COOHwherein R³ is a divalent group, selected from the group consisting of asaturated, branched or straight-chain, aliphatic or cycloaliphatic grouphaving 2 to 13 carbon atoms, (preferably having 2 to 6 carbon atoms), anaromatic hydrocarbon group, optionally substituted by alkyl groups,having a total of 6 to 13 carbon atoms (preferably having 6 to 10 carbonatoms), and an unsaturated, straight-chain or branched, aliphatic grouphaving 2 to 13 carbon atoms (preferably having 2 to 6 carbon atoms).

Examples therefor are maleic acid, fumaric acid, succinic acid,terephthalic acid, isophthalic acid, adipinic acid, glutaric acid,azelaic acid and o-phthalic acid.

However, higher functional polycarboxylic acids, i.e. polycarboxylicacids having more than two (however, preferably not more than six)carboxyl groups per molecule may also be used.

Examples of higher functional polycarboxylic acids are tricarboxylicacids, such as trimellitic acid, tricarballylic acid, trimesic acid orhemimellitic acid, tetracarboxylic acids, such as pyromellitic acid, orpolycarboxylic acids having more than three carboxyl groups such asmellitic acid.

Polycarboxylic acids having at least two carboxyl groups andadditionally one or more OH groups such as malic acid, tartaric acid,meso-tartaric acid, paratartaric acid or citric acid may also be used ascomponent (iv).

The polycarboxylic acids (iv) may be used in form of the free acids oras an anhydride or ester of simple C₁-C₄ alcohols for the preparation ofthe polyester resin.

It is particularly preferable to use dicarboxylic acids or theanhydrides or C₁-C₄ esters thereof as component (iv).

A mixture of at least two different polycarboxylic acids (preferablydicarboxylic acids) is used as component (iv) in another preferredembodiment. In this embodiment the average functionality is preferablyat least 2.0, more preferably 2.0 to 3.0.

A composition in which the amount of the component (iv) is about 10 to40 wt. % based on the sum of all components (i) to (iv) is preferablyused for the preparation of the polyester resin.

Preparation of the Resin

The esterification of the alcohol and acid components is usuallyconducted in the temperature range of from 180 to 260° C. withelimination of water, which is removed from the reaction mixture bydistillation. According to common practice in resin chemistry, removalof this water may also be promoted by azeotropic distillation or byvacuum.

The stoichiometric ratios are adjusted in a manner known to the personskilled in the art such that polyester resins are obtained having acidnumbers from 5 to 20 and amounts of hydroxyl from 1 to 8 wt. %.

The amount of hydroxyl is determined according to common practice in thefield with acetic anhydride. The determination of the acid number isconducted according to DIN 53402.

The polyester resin may be pre-crosslinked with isocyanates to increasethe starting molecular weight and improve the physical drying oraccelerate drying. However, not more than 30% of the available hydroxylgroups should be reacted in the pre-crosslinking of thehydroxy-functional polyester resin. The isocyanantes described below forcomponent (B) may be used for the modification. The reaction withisocyanate is usually conducted in the temperature range of from 10 to70° C., preferably from 20 to 50° C.

Surprisingly, the polyesters prepared according to the present inventionare emulsifiable in water after the neutralization with ammonia oramines usually without the addition of solvents, in particular withoutthe addition of emulsifiers. The resulting emulsions usually have asolids content of from 20 to 70%, preferably from 30 to 55% and a pHvalue of 6 to 9 and are characterized by excellent storage stability.

The neutralization may be achieved by addition of a small amount of aneutralizing agent, wherein a portion or all of the acid groups presentin the resin are neutralized. Suitable neutralizing agents, which may beused according to the present invention, include ammonia, ammoniumhydroxide and primary, secondary and tertiary mono- or polyamines,including hydroxyl amines and in particular lower alkyl amines, such asethyl amine, butyl amine, dimethyl amine, diethyl amine, dimethylethylamine, dimethylisopropyl amine, diethanol amine, triethanol amine orbutanol amine. Amines, which are volatile at temperatures below 180° C.,preferably below 120° C., are preferred. Ammonia, triethyl amine,dimethyl amine, dimethylisopropyl amine, dimethylethanol amine, ethanolamine, diethanol amine, triethanol amine, amino propanol ordimethylamino propanol are particularly preferred amines. The amines maybe added in an undiluted form, whereby essentially water-free,neutralized resins are obtained, which may be virtually unlimitedlydiluted or dispersed in water. Alternatively, the resins may beneutralized by addition of an aqueous solution or dispersion of amines.Likewise, inorganic neutralizing agents, such as potassium or sodiumhydroxide or carbonates may be used for neutralization.

The resin is then adjusted to a desired viscosity in water, whereby anaqueous dispersion of from 5 to 55 wt. %, preferably from 25 to 55 wt.%, solid resin (non-volatile) is obtained.

The polyester resin emulsions described can be formulated as pigmentedand non-pigmented mother paints using the additives conventionally usedin the paint industry, such as pigments, fillers and auxiliaries. Theaddition of cosolvents is additionally possible to achieve improvementof the flow, the wettability and the surface quality.

Isocyanate Component (B)

The isocyanate component of the two-component water-based paint systemof the present invention comprises a saturated aliphatic, cycloaliphaticor aromatic polyisocyanate, which preferably has an averagefunctionality of at least two, in particular 2.0 to 4.5.

Suitable isocyanates comprise the diisocyanates and/or higher functionalpolyisocyanates conventionally used in the field. They may be usedseparately or as a mixture.

Examples of suitable isocyanates are:

-   Toluene-2,4-diisocyanate, toluene-2,6-diisocyanate,    3-phenyl-2-ethylenediisocyanate, 1,5-naphthalenediisocyanate,    cumene-2,4-diisocyanate, 4-methoxy-1,3-diphenyldiisocyanate,    4-chloro-1,3-phenyldiisocyanate, diphenylmethane-4,4′-diisocyanate,    diphenylmethane-2,4′-diisocyanate,    diphenylmethane-2,2′-diisocyanate, 4-bromo-1,3-phenyldiisocyanate,    4-ethoxy-1,3-phenyldiisocyanate, 2,4′-diisocyanatodiphenylether,    5,6-dimethyl-1,3-phenyldiisocyanate,    2,4-dimethyl-1,3-phenyldiisocyanate, 4,4-diisocyanatodiphenylether,    4,6-dimethyl-1,3-phenyldiisocyanate, 9,10-antracenediisocyanate,    2,4,6-toluenetriisocyanate, 2,4,4′-triisocyanatodiphenylether,    1,4-tetramethylenediisocyanate, 1,6-hexamethylenediisocyanate,    1,10-decamethylenediisocyanate, 1,3-cyclohexylenediisocyanate,    4,4′-methylene-bis(cyclohexlisocyanate), Xylenediisocyanate,    1-isocyanato-3-methylisocyanato-3,5,5-trimethylcyclohexane    (isophorone diisocyanate), 1,3-bis(isocyanato-1-methylethyl)-benzene    (m-TMXDI), 1,4-bis(isocyanato-1-methylethyl)benzene (p-TMXDI) or    trimethylhexamethylenediisocyanate.

However, oligomeric polyisocyanates such as those used in conventional,solvent-containing two-component paints are particularly suitable. Theseare for example pre-adducts, isocyanurates, uretdiones, allophates, etc.based on hexamethylene diisocyanate, isophorone diisocyanate andtolylene diisocyanate.

In addition, oligomeric polyisocyanates are also suitable, which containhydrophilic components and were developed in particular for the use inwater-based paint systems. Such isocyanates are described for example inEP-A-540 958, EP-A-645 410, EP-A-754 713 and EP-A-697 424.

In a preferred embodiment of the present invention only saturated,aliphatic and cycloaliphatic isocyantates are employed, i.e. suchisocyanates, the isocyanate groups of which are only bound to saturatedcarbon atoms, wherein aromatic groups may be additionally be present,which, however, do not bear any isocyanate groups themselves.

Organic solvents, such as esters, ketones or ether acetates may be usedto facilitate the incorporation of the isocyanate component. The amountof solvent usually used is in the range of from 10 to 40%, based on theisocyanate used.

Processing of the Paint

The isocyanate component described is mixed homogenously with thepolyester resin emulsion or the mother paint a short time before theprocessing. Organic solvents, such as esters, ketones or alkylatedesters of multivalent alcohols or oligomeric polyglycols, such asmethoxypropyl acetate or methoxydiglycol acetate may also be added tothe isocyanate component to facilitate the incorporation thereof

The amount of solvent used is usually in the range of from 0 to 40 wt. %based on the isocyanate.

The mixing ratio of mother paint and isocyanate curing agent depends onthe amount of hydroxyl in the polyester resin and the amount of NCO inthe isocyanate. The stoichiometric ratios are calculated according tothe so-called isocyanate base value. This defines the amount ofpolyisocyanate, which is equivalent to 100 parts by weight of thecomponent containing hydroxyl groups.

${{Isocyanate}\mspace{14mu}{base}\mspace{14mu}{value}} = \frac{42 \times 100 \times {OH}\mspace{14mu}\%\mspace{14mu}{of}\mspace{14mu}{the}\mspace{14mu}{polyol}\mspace{14mu}{component}}{17 \times {NCO}\mspace{14mu}\%\mspace{14mu}{of}\mspace{14mu}{the}\mspace{14mu}{isocyanate}\mspace{14mu}{component}}$

Depending on the desired properties, the amount of curing agent may bevaried considerably. In water-based paint systems in practicesignificantly higher amounts of isocyanate are commonly calculated. Forexample, excesses of isocyanate of 20 to 70% are used.

The mixtures of mother paint and isocyanate component have a pot life of10 min to 6 h at room temperature. The curing of the applied paint layermay be conducted either at room temperature or by forced drying at anelevated temperature, for example at 80 to 120° C.

The curing reaction can be accelerated with the catalysts conventionallyused in the polyurethane chemistry, such as for example metal salts oramines.

Surprisingly, paint layers of more than 120 to 150 μm may be achievedwith the two-component water-based paint systems according to thepresent invention without undesired formation of bubbles. These paintlayers are characterized by high gloss and very good mechanicalproperties, such as hardness, elasticity, adhesion and in particular byexcellent resistance to yellowing and UV.

The invention is further illustrated by the following, non-limitingexamples.

EXAMPLES Example 1

Preparation and Processing of a White Paint

a) Preparation of a Polyester Resin Component (A)

1.67 kg glycerine, 12 kg pentaerythritol, 4.3 kg polyethylene glycol, 10kg phthalic anhydride, 3.6 kg isophthalic acid, 9.1 kgp-tert-butylbenzoic acid and 7.9 kg 2-ethylhexanoic acid are heated withstirring to 240° C. and the resultant reaction water is distilled. Thecharge is kept at 240° C. until an acid number of 12 mg KOH/g isobtained.

The reaction mixture is neutralized with triethyl amine and emulsifiedin 52 kg water. An emulsion of fine particles having a solids content ofabout 43% and a pH value of 7 results.

b) Preparation of a White Paint

Using the emulsion of the polyester resin described in example 1a), awhite paint is prepared according to the following formation:

A 60.0 parts by wt. polyester resin emulsion example 1a) B 27.8 parts bywt. titanium dioxide C  0.7 parts by wt. additive for dispersion(ethoxylated fatty alcohol) D  8.5 parts by wt. distilled water

The preparation of the paint is conducted as usual in an agitator ballmill.

c) Curing of the Paint

The mother paint prepared according to example 1b) is mixed before theprocessing in a ratio of 4:1 with an isocyanate curing agent having thefollowing composition:

70.0 parts by wt. oligomeric isocyanate based on hexamethylenediisocyanate 30.0 parts by wt. methoxypropyl acetate

The mixture has a pot life of about 3 h and can be processed to a drylayer thickness of more than 150 μm without the formation of undesiredbubbles due to the development of CO₂.

The completely cured paint is characterized by high gloss, excellentresistance to yellowing as well as good hardness and elasticity.

In the accelerated weatherability test (1000 h QUV according to DIN53384) no loss of gloss (method according to Gardner, 60°) and novisible yellowing was detected.

Example 2

Preparation of a Two-component PU Clear Paint

87.0 parts by wt.  emulsion according to example 1-a) 2.0 parts by wt.flow additive based on polysiloxane 2.0 parts by wt. butyldiglycolacetate 9.0 parts by wt. waterare homogeneously mixed for the preparation of a two-component PU clearpaint. The isocyanate component from example 1-b) is admixed in a ratioof 3:1 before processing.

This clear paint mixture can also be processed to a dry layer thicknessof up to 150 μm without formation of bubbles and is characterized byexcellent UV-resistance and high gloss.

In the accelerated weatherability test (1000 h QUV according to DIN53384) no loss of gloss (method according to Gardner, 60°) and novisible yellowing was detected.

Example 3

2.5 kg trimethylol propane, 4.1 kg polyethylene glycol, 14.8 kgisophthalic acid, 9.1 kg p-tert-butylbenzoic acid and 8.0 kg2-ethylhexanoic acid are heated with stirring to 240° C. and theresultant water is distilled. The charge is kept at 240° C. until anacid number of 14 mg KOH/g is obtained.

The reaction mixture is neutralized with triethyl amine and subsequentlyemulsified in 55 kg water and the solids content of the emulsion isadjusted to 43%.

Using this emulsion, paints analogous to those of examples 1 and 2 wereprepared.

In the accelerated weatherability test (1000 h QUV according to DIN53384) no loss of gloss was measured (method according to Gardner, 60°)and no visible yellowing was detected.

Comparative Example

10 kg peanut oil, 3.8 kg polyethylene glycol, 9.5 kg pentaerythritol arekept for 3 h at 230° C. Subsequently, 12.6 kg phthalic anhydride and 3.8kg pentaerythritol are added and esterified at 240° C. with eliminationof water until an acid number of 13 mg KOH/g is obtained. The resultantreaction product is neutralized with triethyl amine and emulsified in 55kg water.

Using this emulsion, paints according to examples 1 and 2 were prepared.

In the accelerated weatherability test (1000 h QUV according to DIN53384) a loss of gloss (method according to Gardner, 60°) of about 25%for the white paint (according to example 1) and 20% for the clear paint(according to example 2), as well as a just visible light yellowing inboth cases were detected.

1. A two-component water-based paint system, comprising: a polyesterresin component (A) that is an aqueous emulsion of a hydroxy-functionalpolyester resin, which does not contain any ethylenically unsaturatedmonofunctional carboxylic acid moieties, and which is obtained byreaction of a composition, which comprises (i) at least onelow-molecular polyvalent alcohol having at least two hydroxyl groups permolecule, (ii) at least one polyether polyol, (iii) at least onemonofunctional saturated aliphatic, cycloaliphatic or aromaticcarboxylic acid, and (iv) at least one polycarboxylic acid having atleast two carboxyl groups; and an isocyanate component (B); thepolyester resin component (A) and the isocyanate component (B) beingprovided as separate components suitable for mixing together by anapplicator for application to a substrate, the resulting mixture havinga pot life such that the mixture must be applied to the substrate beforethe hydroxy-functional polyester resin and the isocyanate component havefully reacted, wherein the resin is additionally modified by reactionwith isocyanate prior to mixing the polyester resin component (A) andthe isocyanate component (B) to form a mixed paint system.
 2. Thetwo-component water-based paint system according to claim 1, whereinsaid component (i) is a mixture of at least two different polyols eachhaving at least two hydroxyl groups per molecule and the averagefunctionality is at least 2.0.
 3. The two-component water-based paintsystem according to claim 1, wherein said component (iii) is selectedfrom compounds of the general formulaR²—COOR′ wherein R² is an aromatic, optionally substituted bystraight-chain or branched alkyl groups, hydrocarbon group or astraight-chain or branched saturated aliphatic or cycloaliphatichydrocarbon group, and R′ is a hydrogen atom, a straight-chain orbranched C₁-C₄ alkyl group or a —(CO)R² group.
 4. The two-componentwater-based paint system according to claim 1, wherein said component(iii) is a mixture of at least two different saturated monocarboxylicacids.
 5. The two-component water-based paint system according to claim1, wherein said component (iv) is a mixture of at least two differentpolycarboxylic acids having each at least two carboxyl groups permolecule, and the average functionallity is at least 2.0.
 6. Thetwo-component water-based paint system according to claim 1, wherein thecomposition has 10 to 40 wt % of component (i), 3 to 15 wt % ofcomponent (ii), 10 to 40 wt % of component (iii) and 10 to 40 wt ofcomponent (iv).
 7. The two-component water-based paint system accordingto claim 1, wherein the amount of hydroxyl of the resin is in the rangeof 1 to 8 wt %.
 8. A method of painting a substrate comprising a)providing an aqueous emulsion of a hydroxy-functional polyester resin,which does not contain any ethylenically unsaturated monofunctionalcarboxylic avid moieties which contains (i) at least one low-molecularpolyvalent alcohol having at least two hydroxyl groups per molecule,(ii) at least one polyether polyol, (iii) at least one monofunctionalsaturated aliphatic, cycloaliphatic or aromatic carboxylic acid, and(iv) at least one polycarboxylic acid having at least two carboxylgroups; b) providing an isocyanate component; c) mixing die aqueousemulsion with the isocyanate component to form a mixed paint system; andd) applying the mixed paint system to a substrate before thehydroxy-functional polyester resin and the isocyanate component havefully reacted.
 9. The method according to claim 8, wherein saidcomponent (i) is a mixture of at least two different polyols each havingat least two hydroxyl groups per molecule and the average functionalityis at least 2.0.
 10. The method according to claim 8, wherein saidcomponent (iii) is selected from compounds of the general formulaR²—COOR′ wherein R² is an aromatic, optionally substituted bystraight-chain or branched alkyl groups, hydrocarbon group or astraight-chain or branched saturated aliphatic or cycloaliphatichydrocarbon group, and R′ is a hydrogen atom, a straight-chain orbranched C₁-C₄ alkyl group or a —(CO)R² group.
 11. The method accordingto claim 8, wherein said component (iii) is a mixture of at least twodifferent saturated monocarboxylic acids.
 12. The method according toclaim 8, wherein said component (iv) is a mixture of at least twodifferent polycarboxylic acids having each at least two carboxyl groupsper molecule, and the average functionality is at least 2.0.
 13. Themethod according to claim 8, wherein the composition has 10 to 40 wt %of component (i), 3 to 15 wt % of component (ii), 10 to 40 wt % ofcomponent (iii) and 10 to 40 wt % of component (iv).
 14. The methodaccording to claim 8, wherein the amount of hydroxyl of the resin is inthe range of 1 to 8 wt %.
 15. The method according to claim 8, whereinthe hydroxy-functional polyester resin is additionally modified byreaction with isocyanate prior to mixing the aqueous emulsion with theisocyanate component to form a mixed paint system.